1. Field of the Invention
The present invention relates to printing apparatus such as back printers or line printers and more particularly to a printing apparatus of the type which uses a type carrier which is constituted by an endless belt, chain or other continuously movable train carrying thereon various letters, numerals and/or symbols to be used for the graphic recording of information.
2. Description of the Prior Art
A printing apparatus known as a line or back printer usually comprises a stationary rear frame structure having a number of printing hammers arranged in a row in a lateral direction of the frame structure and a tiltable support structure positioned in front of the frame structure and having a type carrier supported on top of the support structure. During printing of the printing apparatus of this type, the type carrier is driven to travel in front of the row of the printing hammers with an inking ribbon located between the type carrier and the row of the printing hammers and a printing sheet or a set of printing sheets located between the inking ribbon and the row of the printing hammers. The individual printing hammers are selectively driven to move or turn forwardly against the reverse side of the printing sheet or of the rearmost one of the printing sheets so that the printing sheet or sheets and the inking ribbon are pressed upon between the type carrier and each of the printing hammers driven.
In order that the printing sheet or sheets thus typed be imprinted clearly, it is important that the gap or clearance formed between the type carrier and the row of the printing hammers across the printing sheet or sheets and the inking ribbon be minutely adjusted to suit the thickness of the printing sheet or the set of printing sheets set on the apparatus, the printing sheets being usually superposed on one another with a duplicating carbon paper interleaved between every adjacent two of the printing sheets. Thus, a known printing apparatus of the type described has incorporated therein clearance adjusting means which is adapted to enable the tiltable support structure of the printing apparatus to slightly move toward or away from the rear frame structure so that the above mentioned clearance between the type carrier on the front support structure and the row of the printing hammers within the rear frame structure can be minutely varied depending upon the thickness of the printing sheet or the set of printing sheets and carbon papers to be put to use concurrently on the apparatus.
The printing sheet or the set of printing sheets and duplicating carbon papers is vertically passed through the above mentioned clearance and further between the front end of the rear frame structure and the rear end of the front support structure and is usually stepwise fed upwardly during operation of the printing apparatus. In order to facilitate mounting of the printing sheet or sheets on the printing apparatus, therefore, it is desired that the clearance or any gap between the front and frame structures be enlarged temporarily. The above mentioned known printing apparatus is therefore further provided with means adapted to move or turn the front support structure into an inoperative position forwardly spaced apart from the rear frame structure and to hold the support structure in the inoperative position for maintaining a sufficiently broad gap or clearance therebetween throughout the operation for mounting a printing sheet or sheets on the apparatus.
In a conventional printing apparatus of this nature, however, the position retaining means and the clearance adjusting means are constructed and operate independently of each other. In the absence of mechanical and functional intervention between the position retaining and clearance adjusting means, a printing apparatus arranged with such means tends to be complex in construction and require cumbersome manipulative steps for operating the apparatus with use of any of these means.